Recently, optical disk devices are used as devices for realizing random recording and reproducing a large amount of data. The storage capacity of such optical disk devices can be increased by obtaining a constant linear recording density at any place on a disk by employing a constant linear velocity (CLV) method for accessing information on a disk at a constant relative velocity between a light pickup and an optical disk and at a constant recording data frequency. The CLV method makes the disk have a large capacity but a slow access time because circular tracks on the disk have different numbers of sectors per rotation in proportion to radial position and require correspondingly changing the rotation frequency.
On the other hand, the access time can be shortened by employing a constant angular velocity (CAV) method for accessing information on a disk at a constant recording frequency and a constant disk-rotation frequency. The CAV method can shorten the access time to information on the disk with no need for changing the rotation frequency of the disk. However, the disk has a constant number of sectors per rotation independent of radial positions on the disk and, therefore, the outer circular tracks have smaller linear recording density. The memory capacity of the disk can not be improved by the CAV method.
There has been applied a zone constant angular velocity (ZCAV) method for recording and reproducing data on a disk by rotating the disk at a constant rotation frequency, changing the recording data frequency step by step for respective radial zones. This method divides a surface of the disk into a plurality of radial zones in the radial direction from the outer circular tracks to the inner circular tracks. Respective radial zones have respective quantities of sectors. Each zone has a constant number of sectors per rotation in grooves formed therein. The outer radial zone has a larger quantity of sectors per rotation. Thus, the ZCAV method conducts zoning of the disk surface so as to obtain a substantially constant linear recording density on the disk independent of radial positions thereon. The capacity of the disk and the access time thereon can be thus improved.
In a typical disk type recording medium according to the above-mentioned ZCAV system, a surface of a disk is divided into three radial areas (zone 1, 2 arid 3) numbered from the outer periphery of the disk. Each zone includes a plurality of sectors per rotation of the disk. The number of sectors per groove per rotation of the disk is the same for grooves of the same zone.
Each of areas (zone 1 and zone 2) consists of a plurality of grooves. Each groove is divided into a plurality of sectors (per rotation of the disk). Each sector consists of a header indicating a physical sector address on the disk and a data field wherein recording data will be arranged. In each zone, sectors in respective grooves are radially aligned along boundaries on the disk.
The header is of so-called pit-type that is embossed to shut off the groove by a physical sector address information and has been formed together with the groove in advance.
The header consists of a sector mark indicating the beginning of the sector, a VFO field for pulling a phase by a phase locked loop (PLL) for generating a clock necessary for reproducing the physical sector address, an address mark indicating the beginning of the physical sector address, an address field being a physical sector address, an error detection field for detecting an error.
Describing how the above-mentioned disk of the ZCAV system is treated in a disk recording and reproducing device, first the disk is rotated at a constant rotation frequency independent of its radial position (in other words, the outer zone has a higher linear velocity). Furthermore, a recording or reproducing data frequency relating to a data transfer rate changes zone and recording and producing clock signals are generated and applied for changing a data frequency higher at the outer peripheral side of the disk. Accordingly, the access time for the disk may be shortened since there is no need of changing the disk rotation frequency. In addition, the linear recording density can be kept at a substantially constant on any radial position on the disk by increasing the data frequency with an increase of the linear velocity at the outer zones on the disk.
Various kinds of disk devices have been selectably used for applications. For example, the disk devices of the CLV system are applied for recording successive data (e.g., image data) that requires a large storage capacity rather than accessing speed. On the contrary, the disk devices of ZCAV system are applied for recording and reproducing discrete data randomly on the disk in a computer wherein high-speed random access to the disk is necessarily required. However, these types of available disks are quite different from each other in their formats. Manufacturers must produce various types of differently formatted disks that may confuse users.
A conventional disk recording and reproducing device for use with a conventional disk of the ZCAV method can realize high-speed access to information on the disk but has a decreased data frequency, e.g., a reduced transfer rate at the inner radial side of the disk. The ZCAV system disk is inferior to the CLV system disk in data transfer speed when the disk is used for transferring successive data (e.g., image data) or for backing-up the data.
Furthermore, the disk rotation at its inner side in the ZCAV system is lower than that in the ZCLV system since the former system rotates the disk at a constant rotation frequency and the latter system increases the disk rotation at the inner side than at the outer side. This means that the ZCAV system has a longer time to access a desired sector in a rotation of the disk in comparison with the ZCLV system.
A disk recording and reproducing device which is capable of working with differently formatted disks may be manufactured but is very expensive.
In the disk of the ZCAV system, both side boundaries of sectors (minimal unit to be recorded and reproduced) are aligned into radially extending lines. The number of sectors per rotation (per groove) is the same for every groove in the same zone on the disk. This arrangement is needed because the pre-recorded pit-type header may affect data field with a cross-talk if it neighbors with the data field. Namely, the headers shall neighbor with each other and the data fields shall always neighbor with each other to assure reliable data recording therein.
The radial alignment of sectors may, however, cause limiting the linear recording density lower than the ability of the disk or the disk recording and reproducing device since the number of sectors having a specified physical length (for a specified capacity) per rotation of the disk must be a positive integer.
For example, it is assumed that a disk or a device has the recording density of 0.5 .mu.m per bit, 1 sector is composed of 20000 bits and has a physical length 10 mm. When the sectors of 10 mm in length are allocated to a radial zone at radial position of 30 mm, the circumference is 188.5 mm and the number of allocatable sectors of 10 mm in physical length is about 18.85 (188.5 mm.div.10 mm). A positive integer is 18. Accordingly, 18 sectors shall be practically allocated. With 18 sectors per rotation, the bit size at a radius of 30 mm is determined to be 0.523 .mu.m/1 bit. This figure is lower than by about 5% the maximal recording density (0.5 .mu.m/1 bit) of the disk or the device. This means the reduction of memory capacity of the disk.
It is possible to avoid occurrence of cross-talk from a header to data field by radially aligning sector boundaries in each zone. However, neighboring zones are not aligned at their radial sector boundaries in radial direction on the disk. Namely, two zones are arranged in such a way that a header of one zone is faced to a data field of the other zone. Consequently, cross-talk may occur between the header of one zone and a data field of the other zone. Thus, boundary grooves of neighboring zones cannot be used on the disk, resulting in reduction of the disk memory capacity.
A disk is used for recording data on its grooves. The capacity of this disk can be increased if a pitch between grooves is reduced. However, it is impossible to reduce a distance between grooves since the neighboring headers may interfere with each other.